In this episode, the Kingsgate Footbridge in Durham, the Forth Rail Bridge, and the Alamillo Bridge in Seville, are explored to look into the subject of cantilever bridges. This investigation into the greatest man-made structures of all time explores how new materials and construction techniques have allowed engineers, builders and architects to work to the limits of their ability. The series How Did They Build That? focuses on the buildings that re-wrote the rulebook, and the architects, engineers and builders who made the impossible possible. Published: 8 August 2008